1. Field of the Invention
The invention relates to a DC-DC converter; in particular, to a control circuit, a time calculating unit, and a control circuit operating method operated in a power converter.
2. Description of the Prior Art
In general, in order to speed up the load transient variation of the power converter, the on-time of the switch conducting signal (the width of the pulse signal) will be fixedly enlarged twice or several times. For example, as shown in FIG. 1, when the load increases to heavy-loaded from light-loaded, the output inductor current IL becomes high-level from low-level. The on-time of the switch conducting signal UG (the width of the pulse signal) is enlarged 3 times from original Ton to 3 Ton to recover the rapidly declined feedback voltage FB as soon as possible. FIG. 2 illustrates a schematic diagram of the control logic circuit. As shown in FIG. 2, the comparator 20 outputs a pulse width modulation offset signal PWM_offset to switch the switch 40 to generate the switch conducting signal having 3 times width than the original one.
When a designer designs this system, he/she can determine the width magnification of the pulse signal; however, in practical applications, this default magnification is fixed instead of being dynamically adjusted with different loads, therefore, it lacks of flexibility to use. In addition, the switching between 1 time width and several times width is controlled by the pulse width modulation offset signal PWM_offset outputted by the comparator 20, however, since this offset is not fixed, it is hard to accurately determine whether the switch 40 should be switched. Therefore, it is not easy to control and has poor performance.
Therefore, the invention provides a control circuit, a time calculating unit, and a control circuit operating method operated in a power converter to solve the above-mentioned problems occurred in the prior arts.